Rett syndrome [RTT, MIM 312750] is an X-linked postnatal developmental disorder characterized by loss of acquired skills, impairment of cognitive and motor functions, autonomic dysfunction, ataxia, tremors, seizures, autistic features, and stereotypic hand movements. RTT is caused by mutations in the X-linked MECP2 gene which encodes methyl-CpG-binding protein 2 (MeCP2). MeCP2 is thought to be a transcriptional repressor that links DNA methylation to chromatin modifications. Recently, we also found that MeCP2 interacts with an RNA-binding protein and can affect RNA splicing. We and others have shown that mutations in MECP2 cause a broad spectrum of disorders that display partial features of RTT such as autism, mild mental retardation, movement abnormalities, or seizures. Favorable X-chromosome-inactivation patterns in some of these patients and in partially symptomatic female mice that model RTT led us to propose that the diverse phenotypes of classic RTT result from MeCP2 dysfunction in a particular subset of neurons. Furthermore, we propose that loss of function of MeCP2 in specific neurons causes gene expression and RNA splicing changes that mediate the neuron-specific phenotypes. Lastly, we propose that pharmacologic therapies that target some of the neuron-specific changes linked to distinct phenotypes are likely to modulate some of these RTT phenotypes. The Specific Aims of this project are: (1) To identify the neuroanatomical bases of several key features of RTT by deleting Mecp2 in distinct neuronal populations -- using Cre/LoxP technology-- and characterizing the phenotypes of the conditional mutant mice. (2) To identify MeCP2 targets by evaluating neuron-specific gene expression and splicing pattern changes in Mecp 308/y mice which reproduce RTT phenotypes;we will use a novel approach that employs neuron- specific BACarray lines and new splicing/expression arrays. (3) To conduct preclinical pharmacologic trials targeted at clinically relevant molecular changes (based on Data from Aims 1 and 2) to determine if such therapies will alter the RTT disease course. As a proof of concept, we will use drugs that modulate CRH and AVP activities given our discovery of the potential roles of these two MeCP2 targets in RTT phenotypes. These studies will provide insight about the neuronal subtypes and neurotransmitter systems that mediate certain key features of RTT and related disorders such as autism and X-linked mental retardation. They will also provide the community with a rich resource of neuron-specific gene expression/splicing patterns and how some of these patterns differ in RTT. Last but not least, the data generated under this study have the potential to identify effective pharmacologic interventions that could benefit RTT patients.